A group of common verbs changes its stem vowel in every form except nosotros: almorzar becomes almuerzo, almuerzas, almuerza, almorzamos, almuerzan. Volver, dormir, poder and costar all do it. The endings stay completely regular - only the vowel moves.
Examples
- Almuerzo a la una todos los días.
- I have lunch at one every day.
- ¿A qué hora vuelves del trabajo?
- What time do you get back from work?
- Almorzamos juntos los domingos.
- We have lunch together on Sundays.
The mistake to avoid
Nosotros is the exception: almorzamos, never "almuerzamos".
Where this fits in
Daily routines & habits, Spanish A2: Talk about what you do every day, what time, and how often. Reflexive verbs and frequency adverbs.